Precipitation of crystals from solution is a relatively simple phenomenon that should be explained by changes in concentration, temperature, pH, or other local factors. Which of these factors determines the preferential precipitation of urate crystals at the base of the big toe? Podagra correlates with degenerative joint disease of the toe, often follows abuse of the feet, and classically occurs in the middle of the night. These characteristics suggest that crystals may form in resolving synovial effusions. The urate concentration must transiently rise in such an effusion because water will leave the joint space twice as fast as urate. If the local concentration surpasses the solubility of urate, crystals will form that may than induce acute podagra.